Field
The present disclosure relates to a crystalline form of 2-[(RS)-4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl]nicotinic acid (imazapyr), to its preparation processes and to its use in agrochemical preparations.
Description of Related Art
2-[(RS)-4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl]nicotinic acid (imazapyr) is a potent herbicide. Imazapyr has molecular formula of C13H15N3O3. Its chemical structure is:

Imazapyr is a non-selective herbicide used for the control of a broad range of weed including terrestrial annual and perennial grasses and broadleaved herbs, woody species, and riparian and emergent aquatic species. It controls plant growth by preventing the synthesis of branched-chain amino acid. Imazapyr is absorbed quickly through plant tissue and can be taken up by roots. It is translocated in the xylem and phloem to the meristematic tissues, where it inhibits the enzyme acetohydroxy acid synthase (AHAS), also known as acetolactate synthase (ALS). ALS catalyzes the production of three branched-chain aliphatic amino acid, valine, leucine, and isoleucine, required for protein synthesis and cell growth. The rate of plant death usually is slow (several weeks) and is likely related to the amount of stored amino acids available to the plant. Only plants have ALS and produce these three amino acids, and therefore, imazapyr is of low toxicity to animals (including fish and insects). Animals need these three branched chain aliphatic amino acid, but obtain them by eating plants or other animals.
The commercially available imazapyr, which is usually manufactured by the process described in U.S. Pat. No. 4,798,619, is present in amorphous state. It has been found that imazapyr in amorphous state is not suitable for being used in an economical formulation due to the high tendency of aggregation after a long storage time. Therefore, there is a need to provide a novel form of imazapyr with increased storage stability.